DESCRIPTION (Abstract from Grant Application): Retinitis pigmentosa (RP) represents a major cause of visual loss in the Untied States. The primary focus of this grant since its inception has been on physiological mechanisms of rod loss in children and young adults. Studies proposed in this renewal are motivated by rapid advances in the understanding of processes underlying phototransduction in vertebrate rods. Preliminary results suggest that both activation and inactivation stages of phototransduction can be evaluated in patients through the electroretinogram (ERG). Work completed in the previous cycle provides strong evidence that the leading edge of the a-wave is quantitatively described by a recent model of the activation stages of transduction. We will extend this work with a two-flash paradigm that probes inactivation stages of transduction. The work will focus on patients with known mutations from our large and rapidly growing database. Application of proposed ERG techniques will allow us to determine which defects in activation and inactivation result from specific gene mutations. The goal of the proposed subcontract with Dr. Daiger is to determine the genes and mutations causing autosomal dominant RP (adRP) in these patients. The proposed testing has two components, first, screening for mutations in rhodopsin, peripherin/RDS and other genes causing adRP as they are identified and, second, linkage testing of suitable adRP families. Mutation screening methods include SSCP, Cleavase mismatch detection and genomic sequencing. Linkage testing will be conducted in adRP families with 6 or more affected members using a panel of microsatellite markers within or adjacent to 15 distinct loci causing adRP or allied disorders. By these methods we expect to determine the underlying genetic cause in more than 50% of adRP families. Transgenic mouse technology represents a powerful approach to phenotype-genotype causal relations. The techniques we are developing for studying activation and inactivation mechanisms in RP can be applied to the mouse models. We will evaluate the phenotype of transgenic mice expressing mutations in the retinal degeneration slow (rds) gene associated with adRP, in rod outer segment protein 1 (ROM1) knockout mice, and in digenic L185 rds-/rds+, ROM1-/ROM1+ mice. We will determine whether modifying the lipid environment of the outer segment has an effect on the severity of degeneration in these animal models of RP where the disease-causing mutation affects outer segment structure.